The present invention relates to a method for obtaining a position of an optical center of a spectacle lens, and a method for attaching a lens holder to an uncut lens. The lens holder is a jig attached in advance to a rotational center axis of the uncut lens prior to a process of grinding an edge of a spectacle lens. The present invention also includes an apparatus for attaching the lens holder to the uncut lens before the process of grinding.
A spectacle glass, or eyeglass lens, is prepared by processing an uncut spectacle lens (in general, a so-called round lens having a circular shape) into a shape for fitting into the shape of a spectacle frame, then fitting the cut spectacle lens into the spectacle frame. To prepare the uncut spectacle glass for cutting, it is necessary to conduct a layout analysis for determining the position of the optical lens center based on the eye prescription data (the dioptric power, the cylindrical dioptric power, the distance between the right and left eyes and other like data) and spectacle frame shape data with respect to the person who will be wearing the spectacle glass. In other words, it is important to determine the position of the optical lens center, which is a function of both the prescription of the eyeglass lens and the shape of the eyeglass lens frame, to produce a superior eyeglass lens.
The layout analysis is conducted to ensure that the optical center (in the case of a single vision lens) or the eyepoint (in the case of a multifocal lens) of the spectacle lens is aligned with the center of the pupil of the person who will be wearing a pair of eye glasses or a monocle fitted with properly prepared and cut spectacle lens glass. The layout analysis is needed because it is rather rare for a person to pick out an eyeglass or spectacle frame that has the geometrical center of the spectacle frame shape properly aligned and positioned in line with the person""s pupil center. Therefore, if an uncut spectacle lens is processed merely with the intent of aligning the geometrical center of the lens frame shape with the position of the optical center of the lens, then a problem arises because the pupil center is not necessarily aligned with the geometrical center of the frame and the optical center of the lens. The proper alignment between the optical center of the lens and the pupil center of the spectacle wearer is critical for providing the best vision correction with the least amount of eye strain. Therefore, it is more important to align the optical center of the lens with the wearer""s pupil than it is to align the optical center with the geometrical center of the spectacle frame. To achieve this proper alignment between the wearer""s pupil and the optical lens center, it becomes necessary to move the optical center from the geometrical center of the frame and into alignment with the pupil center during the process of fitting the processed lens into the spectacle frame and adjusting the fit while the spectacle is worn.
Once the layout analysis has been completed, an uncut prescribed lens, which satisfies the conditions determined by the above layout analysis and satisfies the eyeglass prescription required by the person who will be wearing the spectacle glass, is selected and then processed. The processing of the uncut lens is conducted using an apparatus for processing a lens which grinds edge portions of the uncut lens by a grinder or a cutter while the uncut lens is rotated around a specific axis approximately perpendicular to the optical face of the uncut lens. When processing the uncut lens using the apparatus for processing a lens, a lens holder is used. The lens holder is a jig that provides a rotational center axis for the uncut lens and is attached to the uncut lens prior to processing.
Previously, the prior art lens holder was attached at the optical center position of the uncut lens in the case of a single-vision lens. In the case of a progressive multifocal lens or a multifocal lens (typically, a bifocal lens), the lens holder was attached at the xe2x80x9ceyepointxe2x80x9d position of the uncut lens. Therefore, it was necessary to obtain the lens optical center position by measurement so that the optical properties (the dioptric power and other properties) of the uncut lens were confirmed to satisfy the conditions of the spectacle prescription. By determining the optical center position, the position for attaching the lens holder was obtained as well.
A lens meter, which is used for measuring optical properties of a lens such as the dioptric power and the prism dioptric power, has been used to measure the optical center of the uncut lens. To provide a measurement of the optical center position, the lens meter is used to measure the prism value of the lens at positions considered, or estimated, to be close to the optical center and by finding out the position on the lens where the prism value becomes zero, or by calculating the position of the optical center in accordance with a specific equation using the prism value obtained by the measurement.
However, from a practical standpoint it remains a complicated and difficult process to visually measure the prism value with a lens meter at positions considered to be close to the optical center, and it is even more problematic to find the position having a prism value of zero. Moreover, it is not always possible to accurately determine the position of the optical center using this prior art method. The alternate prior art method for obtaining the position of the optical center by measuring the prism value of the lens near, or approximate to, the optical center and then calculating the optical center position in accordance with a specific equation suffers from the fact that the accuracy is different depending on the position of the measurement. The error in calculating the optical center position is great when the location of the measurement on the lens is far from the true position of the optical center. The strength of this prior art method of calculating the optical center position from a measured prism values is that the accuracy error is small when the location of the actual measurement is close to the true position of the optical center. However, the object is to choose a location that is sufficiently close to the true optical center position to provide an accurate calculated optical center position.
Another problem that has recently occurred is that lenses for spectacle frames having certain shapes are difficult to process; mainly, the typical processing methods of the prior art cannot be conducted because the lens holder can not be attached at the optical center. Specifically, as the preference of people who wear spectacle glasses diversifies, spectacle frames having non-traditional shapes, including very small dimensions in the vertical direction, are becoming more popular. When the spectacle frame has a vertical dimension smaller than a specific value, attaching the lens holder to the optical center results in processing interference taking place because a portion of the outer periphery of the lens holder protrudes beyond of the shape, or borders, of the spectacle frame (the shape to be formed by the processing the uncut glass). Consequently, the processing or grinding of the uncut lens glass into one of these non-traditional shapes with an insufficient vertical dimension becomes impossible.
The object of the present invention is to provide a method for accurately and efficiently measuring the optical center of a spectacle lens, wherein the method includes a method or steps for attaching a lens holder to a spectacle lens so that the position of the attached lens holder will not produce processing interference during grinding. The object of the invention includes efficiently attaching the lens holder to the spectacle lens and providing an apparatus for attaching the lens holder to a spectacle lens having characteristics described above.
The first preferred embodiment of the present invention provides a method for obtaining a position of the optical center of a spectacle lens comprising the steps of (1) measuring the optical properties of a spectacle lens at a first measured position of the spectacle lens by using a lens meter for measuring the optical properties of the spectacle lens, wherein the optical properties measured include a prism value; (2) calculating the position of the optical center of the spectacle lens using at least the prism value obtained by measuring the optical properties at the first position, wherein the first calculation involves a specific relational equation, then setting the resultant position, being a first estimated position obtained by calculation, as a first calculated position for subsequent calculation of the optical center; (3) concluding that the first calculated position for the optical center is sufficiently equivalent to the true position of the optical center when a distance between the first measured position and the first calculated position of the optical center is equal to or smaller than a specific reference value; (4) when the distance between the first measured position and the first calculated position of the optical center exceeds the specific reference value, measuring the optical properties at the first calculated position of the optical center using the lens meter followed by calculating a second calculated position of the optical center using values of the optical properties obtained by measuring at the first calculated position, wherein the second calculation involves the specific relational equation; (5) concluding that the second calculated position for the optical center is sufficiently equivalent to the true position of the optical center when a distance between the first calculated position and the second calculated position of the optical center is equal to or smaller than the specific reference value; (6) when the distance between the first calculated position of the optical center and the second calculated position of the optical center exceeds the specific reference value, measuring the optical properties at the second calculated position using the lens meter followed by calculating a third calculated position of the optical center using values of the optical properties obtained by measuring at the second calculated position, wherein the third calculation involves the specific relational equation; (7) conducting further steps in a similar manner to those conducted in the above steps in which it is checked whether a distance between successive positions for calculation of the optical center does not exceed the specific value; and (8) when a distance between an (nxe2x88x921)-th calculated position and an n-th calculated position of the optical center is equal to or smaller than the specific value, determining that the n-th calculated position of the optical center is sufficiently equivalent to the position of the true optical center of the spectacle lens.
The second preferred embodiment of the present invention provides a method for attaching a lens holder to an uncut lens, the lens holder being a jig attached to the uncut lens prior to a process of grinding an edge of the spectacle lens, wherein the lens holder provides a rotational center axis for the uncut lens during the process of grinding, the method comprising steps of: (1) measuring optical properties at a first measured position of the uncut lens using a lens meter for measuring the optical properties of the uncut lens, wherein the optical properties measured includes at least a prism value; (2) calculating a first calculated position of the optical center of the uncut lens using values obtained by measuring the optical properties at the first measured position, wherein the first calculation involves a specific relational equation, then setting the resultant position, being a first estimated position obtained by calculation, as a first calculated position of the optical center; (3) concluding that the first calculated position of the optical center is sufficiently equivalent to the true position of the optical center when a distance between the first measured position and the first calculated position is equal to or smaller than a specific reference value, followed by using the first measured position as the position for attaching the lens holder to the spectacle lens; (4) when the distance between the first measured position and the first calculated position of the optical center exceeds the specific reference value, measuring the optical properties at the first calculated position of the optical center using the lens meter followed by calculating a second calculated position of the optical center using values obtained by measuring at the first calculated position, wherein the second calculation involves the specific relational equation; (5) concluding that the second calculated position for the optical center is sufficiently equivalent to the true position of the optical center when a distance between the first calculated position and the second calculated position of the optical center is equal to or smaller than the specific reference, followed by using the first calculated position of the optical center as the position for attaching the lens holder; (6) when the distance between the first calculated position of the optical center and the second calculated position of the optical center exceeds the specific reference value, measuring the optical properties at the second calculated position using the lens meter followed by calculating a third calculated position of the optical center using values of the optical properties obtained by measuring at the second calculated position, wherein the third calculation involves the specific relational equation; (7) conducting further steps in a similar manner to those conducted in the above steps in which it is checked whether a distance between successive positions for calculation of the optical center does not exceed the specific value; and (8) when a distance between an (nxe2x88x921)-th calculated position and an n-th calculated position of the optical center is equal to or smaller than the specific value, determining that the n-th calculated position of the optical center is sufficiently equivalent to the position of the true optical center of the spectacle lens, and determining that the (nxe2x88x921)th calculated position of the optical center is the position for attaching the lens holder.
The third preferred embodiment of the present invention provides a method for attaching a lens holder according to the second preferred embodiment, but further comprises the step of determining whether processing is possible based upon processing information including the shape to be formed by processing the uncut lens and the shape of a lens buildup area of the lens holder assuming that the lens holder attaches at the determined position for attaching the lens holder, followed by initiation of lens processing.
A fourth preferred embodiment of the present invention provides a method for attaching a lens holder according to any one of the second preferred embodiment and the third preferred embodiment of the present invention, wherein information describing the positions obtained during procedures ranging from the method for determining the first calculated position to the method for determining the position for attaching the lens holder to an uncut lens is maintained as transmittable information so that the information can be used as process control information in a numerical control type processing apparatus.
The fifth preferred embodiment of the present invention provides an apparatus for attaching a lens holder to an uncut lens, the lens holder being a jig attached to the uncut lens prior to a process of grinding an edge of a spectacle lens, wherein the lens holder provides a rotational center axis for the uncut lens during the process of grinding, the apparatus comprising: a computer; a lens meter for measuring optical properties of the uncut lens, the lens meter being connected to the computer in a manner such that information measured by the meter is transmissible to the computer, the measured information comprising measurable optical properties of the lens including a prism value; and a movable table on which the uncut lens to be measured by the lens meter is disposed, and which moves to a desired position in accordance with specific control information comprising the measured information, the table comprising a position measuring device for measuring a position of the table that is operationally connected to the computer to allow information exchange between the position measuring device and the computer, wherein the position measuring device outputs position information to the computer, wherein the computer comprises a program for an information processing method comprising the steps of: (1) outputting a control command to the lens meter and the movable table so that optical properties of the uncut lens are measured at a first measured position under the control; (2) calculating a first calculated position of an optical center of the uncut lens using values obtained by measuring optical properties of the lens at the first measured position in accordance with a specific relational equation and setting the resultant position, being a first estimated position obtained by calculation, as a first calculated position of the optical center; (3) concluding that the first calculated position of the optical center is sufficiently equivalent to the true position of the optical center when a distance between the first measured position and the first calculated position is equal to or smaller than a specific reference value, followed by using the first measured position as the position for attaching the lens holder to the spectacle lens; (4) when the distance between the first measured position and the first calculated position of the optical center exceeds the specific reference value, measuring the optical properties at the first calculated position of the optical center using the lens meter followed by calculating a second calculated position of the optical center using values obtained by measuring at the first calculated position, wherein the second calculation involves the specific relational equation; (5) concluding that the second calculated position for the optical center is sufficiently equivalent to the true position of the optical center when a distance between the first calculated position and the second calculated position of the optical center is equal to or smaller than the specific reference, followed by using the first calculated position of the optical center as the position for attaching the lens holder; (6) when the distance between the first calculated position of the optical center and the second calculated position of the optical center exceeds the specific reference value, measuring the optical properties at the second calculated position using the lens meter followed by calculating a third calculated position of the optical center using values of the optical properties obtained by measuring at the second calculated position, wherein the third calculation involves the specific relational equation; (7) conducting further steps in a similar manner to those conducted in the above steps in which it is checked whether a distance between successive positions for calculation of the optical center does not exceed the specific value; and (8) when a distance between an (nxe2x88x921)-th calculated position and an n-th calculated position of the optical center is equal to or smaller than the specific value, determining that the n-th calculated position of the optical center is sufficiently equivalent to the position of the true optical center of the spectacle lens, and determining that the (nxe2x88x921)th calculated position of the optical center is the position for attaching the lens holder.
Further objects features and advantages of the present invention will become apparent from the Detailed Description of Preferred Embodiments, which follows, when considered together with the attached drawings.